Ethernet using copper cabling and backplane may use several different operational modes for communication links. The various operational modes may have different link speed, line encoding, and other characteristics. Certain Ethernet standards define methods to autonegotiate one of several specifically enumerated physical layer technologies and operational modes to be used for a particular communication link. One such autonegotiation protocol is defined in Clause 73 of the IEEE standard 802.3 (2012). For copper cable applications, the lowest-speed operational mode available for clause 73 autonegotiation is 40-gigabit communication over four physical lanes (40 GBASE-CR4). Additionally, clause 73 always attempts to activate the fastest common communication technology between the link partners.
Lower link speeds may be desirable for certain applications, such as for low-power applications including wake-on-LAN (WOL) applications, or for use with broken or lower-quality media (i.e., cable). For example, lower communication speed may be desirable when one of several physical lanes typically used is broken or otherwise not operable. Lower link speeds may be manually reconfigured using firmware or software solutions executed by both of the link partners. Successful manual reconfiguration of link technology may require close synchronization of changes made to both link partners.